Conventionally, as apparatuses that carry out communication through optical fibers, optical transceiver modules have been known that carry out transmission and reception of signals using two wavelengths of light, λ1 and λ2, in the range of 1300-1600 nm.
Such optical transceiver modules are provided with a lens between the end surface of the optical fiber and a light receiving element or a light emitting element, and on the optical surface of the lens, provided are thin films or a diffraction structure that change the optical path depending on the wavelength (see, for example, Patent Documents 1-3). In the interior of the optical transceiver module, not only light of wavelength λ1 emitted from the end surface of the optical fiber is incident on the light receiving element, but also light of wavelength λ2 emitted from the light emitting element is incident on the end surface of the optical fiber.
An antireflection coating is provided, in order to increase transmission, on an optical element that allows passing low wavelength light of 650 nm or 780 nm through them.
However, when an antireflection coating known in the art for low wavelength light of 650 nm or 780 nm are merely applied as an antireflection coating provided for an optical element used for light of wavelength of 1300-1600 nm, the transmittance can be improved, however, because of the longer wavelength, the thicknesses of the layers constituting the antireflection coating become larger compared to those of known antireflection coatings. As a result, if the body of the lens is made of plastic, the distortion due to internal stresses within the constituting layers become larger when the shape of the lens body changes due to changes in temperature or humidity, resulting in forming cracks. Accordingly, the durability of the lens is reduced.
Patent Document 1: Japanese Patent Publication Open to Public Inspection (hereafter referred to as JP-A) No. 2000-180671
Patent Document 2:JP-A No. 2004-37928Patent Document 3:JP-A No. 2003-344715